Hydkaulic drive



Aug. 7, 1951 c. H. SCOTT 2,563,622

HYDRAULIC DRIVE Filed Jan. 23, 1948 6 Sheets-Sheet l Aug. 7, 951

Filed Jan. 23, 1948 C. H. SCOTT HYDRAULIC DRIVE INVENTOR:

CHARLES H. SCOTT,

ATTO R N EY Aug. 7, 1951 C, H SCOTT A 2,563,622

HYDRAULIC DRIVE Filed Jan. 25, 1948 6 Sheets-Sheet Ellllll I I yl/M F I G 5' lNVENTOR:

- CHARLES H. SCOTT.

ATTORNEY Aug. 7, 1951 l C. H. SCOTT 2,563,622

HYDRAULIC DRIVE Filed Jan. 23, 1948 6 Sheets-Sheet 4 INVENTORI CHARLES H.scoTT, BY

ATTORNEY C. H. SCOTT HYDRAULIC DRIVE Aug. 7, 1951 6 Sheets-Sheet 5 Filed Jan. 23, 1948 INVENTOR CHARLES H. SCOTT,

'l f. l1.".

ATTORNE .WM ...mm l

Aug. 7, 195] C, H, SCQTT 2,563,622

HYDRAULIC DRIVE Filed Jan. 25, 1948 6 Sheets-Sheet 6 FIG. lo. UW'

INVENTORE CHARLES H. SCOTT, BY

ATTORNEY `more feet.

Patented Aug. 7, 1951 HYDRAULIC DRIVE Charles Harold Scott, Westport, Conn., assigner to The Dorr Company, Stamford, Conn., a corporation of Delaware Application January 23, 1948, Serial No. 4,042

(Cl. 21o- 55) 6 Claims. l

The general object of the present invention is to provide a simple and effective hydraulic drive mechanism of novel form for rotating a structure about an axis at a relatively low angular velocity but against a relatively strong opposing force or load torque.

The invention was primarily devised for use in rotating the mud rakes of large sedimentation units used for thickening and desilting purposes. The large sedimentation units with which the present invention may be used with special advantage, have diameters varying from about one hundred feet up to about two hundred Fifty or Each such unit is usually provided with a central bottom outlet for the discharge of solids or mud deposited on the bottom wall of the sedimentation chamber or basin and slowly worked to the central outlet by mud rakes forming part of a structure mounted for rotation about the central vertical axis of the sedimentation chamber. While the rotative movement of the mud rakes is 'quite slow, the substantial radial extent of the mud rake arms, and the mud density and volume are such that a large driving torque must be impressed on the rotating structure to maintain it in rotation at a suitable speed. Heretofore, it has been customary to rotatethe mud rakes of large sedimentation devices by an electric motor connected lto the rotating structure through speed reducing toothed gearing of a relatively heavy and expensive type.

A primary object of rthe invention is to provide a mechanism comprising pistons working in hydraulic cylinders and pawl and ratchet means through which said pistons impress continuous rotative forces on a rotatable structure, and sufnciently simple, reliable and eective and relatively inexpensive to construct and operate lso that it may be used with advantage in place of a driving mechanism including speed reducing gearing of the type heretofore customarily einployed.

A speciiic object 'of the invention is to provide a hydraulic driving mechanism in which each pawl actuating cylinder is pivoted at one end to the supporting structure so that the stem or connecting rod rigidly connected to thepiston working insaid 'cylinder may be directly connected to the actuating pawl of the pawl and ratchet mechanism in one form of the invention, and another :form of the invention may be Adirectly connected to the free end of a 'ratchet lever pivoted to turn about the axis 'of the rotating structure.

The present invention 1s welladapted for use 2 with the rotating structure and rotating mechanism of a relatively large sedimentation unit, supported in either of the two ways heretofore customary, namely, either by means of a supporting structure comprising a bridge or beam above the sedimentation chamber and extending diametrioally across the latter and supported at its ends, or by means of a vertical center pier or column extending up through the sedimentation space to a height suitably above said space. By way of example and illustration, it is noted that the bridge type supporting means for the rotating structure of a large sedimentation unit is shown in my prior Patent 2,087,725 of July 20, 193'?, and that support of the rotating structure and rotating mechanism of a large sedimentation device by a center pier or column, is disclosed in my prior Patent 2,086,394 of July G, 1937.

One speciic object of the invention is to provide a mechanically simple hydraulic drive of the pawl and ratchet type characterized by the simple and eiTective character of the valve mechanism by which a small number of pawls, usually not more than two, each with an individual hydraulic actuating cylinder, are employed to maintai'n the rotating structure of the sedimentation device in slow but continuous rotation.

Another `specific object of the invention is `to provide simple and effective means, comprising pressure relief valves, for limiting the maximum fluid `pressures transmited to the hydraulic cylinders to prevent injury to the apparatus when the resistance to the piston movement becomes unduly high.

rlhe various features of novelty Vwhich characterize my invention are pointed out with particularity in the claims annexed to and forming `a part of this speciiication. `For a better understanding of the invention, however, its advantages, and specic objects attained with its use, reference should be had to the accompanying drawing and descriptive matter in which I have illustrated and described preferred embodiments of the invention.

Fig. l is a plan view of a sedimentation `unit with parts broken away;

Fig. 2 is an elevation in section on the line 2 2 of Fig. l;

Fig. 3 is -a plan view on a larger scale of aportion of the apparatus shown in Fig. l, with parts broken away and in section;

Fig. Il is a plan view on a still larger scale of a portion of the apparatus show-nin Figs. 1 and 3 with parts broken away;

Fig. is an elevation with parts in section on the line 5 5 of Fig. 4;

Fig. 6 is an elevation partly in section of valves and valve operating mechanism shown in Figs. 1 and 4 as seen from one side;

Fig. '7 is an elevation of the apparatus shown Vin Fig. 6 as seen from its other side;

Fig. 8 is an operation diagram illustrating the operation of the apparatus shown in Figs. 1-7;

Fig. 9 is a somewhat diagrammatic plan View illustrating a modification of the apparatus shown in Figs. 1-8;

Fig. is a section on the line lll--I of Fig. 9, and A Fig. 11 is a section on the line II-II of Fig. 9.

In the embodiment of the invention illustrated by way of example in Figs. 1-8 of the accompanying drawings, I represents a cylindrical sedimentation or thickening chamber or basin which is shown as surrounded by the cylindrical wall 2 of a vertically disposed tank. The latter is open at its upper end and has a bottom Wall 3 formed with a central conical depression 4 which serves as a mud outlet to which is connected a mud pipe 5 through which settled solids are withdrawn. Mud pumping means (not shown), of the usual type may be used to draw the mud away from the chamber I through the pipe i. The solids accumulating in the lower portion of the chamber or basin I, are worked to the mud outlet 4 by rake arms ii carrying rakes 5' which may be of customary form. The rakes 6 have their inner ends secured to and are supported by a rotating element shown as a vertical shaft 'I coaxial with the chamber I.

The shaft I is suspended from a stationary framework above the chamber or basin I which, as shown, comprises a bridge or composite frame structure including a pair of parallel beams 8 which extend across the tank and are supported at their ends by a stationary framework 8. The beams 3 also support the mechanism for rotating the shaft The shaft 'I has its upper end portion journalled in upper and lower sleeve bearings II) and II, which are respectively mounted on and supported by upper and lower channel bar beams I2 and I3. Those beams are parallel to, above, and centrally disposed in the space between, the main supporting beams 8. The beams I2 and I3 are supported by a framework which includes bottom beams I4 transverse to and directly supported by the beams 8, and vertical beams I5. The weight of the shaft I and rake arms 6 is supported by a thrust bearing, shown as comprising a collar I5 pinned or otherwise secured to the upper end of the shaft 'I, and having its underside in engagement with the upper side of the web or body portion of the beam I2, which has downwardly extending side flanges. The beams I2 and I3 are formed with central apertures through which the shaft 1 extends. In lieu of the simple thrust bearing shown in Fig. '7, use will ordinarily be made, particularly in relatively large sediment units, of a thrust bearing including roller elements which may be of the general character of those shown in my above-mentioned prior patents. The above-mentioned structural elements I-I6 are conventional in form and arrangement, and comprise nothing claimed as novel herein.

In the form of the invention illustrated in Figs. 1-8, the rotating structure comprising the mud rakes 8 and shaft 'I is rotated by a hydraulic motor drive mechanism, including a ratchet wheel I'I rigidly attached to and forming a part of the CII rotating structure, driving pawls I8 and I8 carried by ratchet levers I9 and I9', and hydraulic cylinders 28 and 2D. As shown, the ratchet wheel I'I is in the form of a spur gear and is mounted on and secured to the shaft 'I and is located in the space between the upper and lower beams I2 and I3. The wheel I'I is adapted to be operatively engaged by the pawl I8 during periods which alternate with, and preferably overlap periods during which the wheel I'I is operatively engaged by the pawl I8. The pawl I8 is mounted on a pivot 2| having its ends secured in upper and lower portions of the lever I9. The lever I8 has one end journalled on the shaft and has its opposite end connected through a pivot 22 to the piston 23 of the hydraulic cylinder 2li. The cylinder 28 has end members or heads 24 and 25. The end member 24 has an extension, shown in Fig. 2 as comprising two spaced apart ears 26 perforated to receive a transverse pivot pin 21 which pivotally connects the corresponding end of the cylinder 28 to the upper and lower beams I2 and I3. The end member 25 is formed with an axial passage for the piston rod 23 which is secured to the adjacent end of the piston 28 working in thecylinder 20. A stuffing `box 29 is provided at the outer end of the head 25 to prevent leakage out of the cylinder 20 along the piston rod 23. The previously mentioned pawl I8', ratchet lever I9 and cylinder 20 are associated with parts 2l to 28' which may be, and as shown are similar to the previously mentioned parts 2I--29, respecttively. Y

rIhe lever I9 is given successive angular movements in the clockwise direction, as seen in Fig. 3, by pressure fluid, ordinarily oil, supplied to the piston chamber in the cylinder 20 through a pipe 30 connected to the pivoted or rear end of the cylinder 28, and is given counter-clockwise movements alternating with the clockwise movements by pressure uid intermittently supplied to the opposite or front end of the cylinder 28 through a pipe 3l. The pipes 38 and 3l include flexible portions to accommodate the oscillating movements of the cylinder 28 about its pivot 22. The lever I9 is given alternating clockwise and counter-clockwise adjustments by pressure fluid intermittently supplied to the rear and front ends, respectively, of the piston chamber in the cylinder 28 by pipes 30 and 3|', similar to the pipes SI1 and 3l. The clockwise and counterclockwise movements, of the levers I9 and I 9 are driving and return strokes, respectively. The supply of pressure fluid to, and its discharge from the cylinders 2d and 28 through the pipes` 30, 3| 30' and 3l is controlled by a valve mechanism illustrated diagrammatically in Fig. 8, and hereinafter described. In Fig. 8, the piston 28 working in the cylinder 20 and the piston 28 working in the cylinder 28 are shown in the p0-A sitions through which they respectively move during an intermediate portion of a working stroke of piston 28 and a return stroke of piston 28.

During each driving or working stroke of either lever I9 or I8', the corresponding pawl I8 or I8 engages the wheel I as does the pawl I8 shown in 3. As the idle stroke of each ratchet lever is initiated, the corresponding pawl is cammed out of engagement with the wheel I I and is then free to occupy the position relative to the wheel in which the pawl I8 is shown in Fig. 3, until near the end of said idle stroke. In the nal portion Qi the idle stroke of each ratchet lever, the cor- 5 r'esp'ondirigpawlj or I8 is mov into operative eflgkigmelillli. .Uhfh 0f tfl Wheel l", bl the corresponding b ias spring 32er 32. Only as shovyfn, eacli ybias spriijig has one en d Connected to lthe aqjaceriterosS-beain I4 and has its other eijd ooriiieetedthroug a chairi or 33" to the tail ofthe corresponding pawl. The bias springs apri as soi'ated chains are so proportioned and arranged. that each bias spriig is piit uridr teisioii 01H15" ,n/Tr the @lid f the returi Stroke of the eorlespohdirig lever. The teiisr`r1-of eaizh bia-S spriril'g relier/ed lafter short iriitial portion of the worlgiigstroke of tlie eorrespondiiig ratchet ler/er, hiitdiiririg lie remainder of that Working stroke the c` spboling I'awl is held in engag`e meit with the corresponding tooth of the Wheel L1 by tri driving force inem being transmitted. by

1, The y'alve `triechafriism iiereinaftel described, so Varies the flow of pressure uid through 'the pipes lll, l lifarii Sl pressli're fluid is supplied te th A cylincleijs @and 20 throlrgh the pipes v:si: nfd il', rfe's'iietiveim during periods which alternate Vwith periods diirirg which pressure am' is sup'piii to the `cyiiiidjc-Ji-s 2e and -2n' thijiieii'fthefpipes l `and 350', rsp'eetvely. During the periods which pressure i'uid is beihg spplid to fliigides Zilnadll through the pipes prssii fiiflidisbeing exhausted from the cylinders 2li and 2Q through the vpipes 3l 'arid S: Similarly', the periods in Wlji'el presn sure fluid -rbeing supplied to the oyliiifier's an@ 2G through the pipes 3j and 3B', piessiire qid 'is be'ig feihatisted freni the Cylinders tlrogh tlfi'ppes 3l) arid 3 l respectively Siiee the idle stroke 'of eah of the pistoris 28 iid 28 is effected bythe passage if pressure Quid into oyl'iider 'spatie surroundiiig the oorrsporidiiig pieten Siem 2'?, 6r 233 vgiiiime gif trie pressure iiidrequred to ei'eetthe return st'r'l'e is sbstartially sijall'eig than the ifoliiiii'e oi presfluid rc'liri to effet Worlirig Stroke. ii seqierioejth dlefstroke oi leach of the pistons 2 an 28' may be Veffected in less time than is req .reti foi` the Wbrki'g `'Sti'roke ef tlie piston. The lirieqiiai speeds with which the werking :ma ijdlestrlisare 'eie'ted facilitate the use of the 'desirable 'mode `of obere-tion in which the Workiiigfstijole of a'lj. of the iistoris 2S arid 23 is iitiated b'eretli'e Working stroke 'of the other Tine valve yrriechariisirr controlling the oper# ation 'of tl'ieliydraulie cylinders 2i) arid 21 c'onprises "similar `Yali/"es 34 'ariel 34( and means tlir'oilglji which they are adjusted by, 'arid iii lsyjiieh'itiiiism with, the rotative miveiifeiiisei tri iippiiri'q karig iajted by a shaft 4U, as iisly egiplaiiied.' The vali/e Sii may be The plungers 0f U, equi im axis di Ime shari in foidsmiieihiiig less `tlvi'anw18,92 arid ase ond are shaped edge @gif te i1. eine frati@ of gears v Il' arid 4 9 isjnot 'criticak but it is 'noted 40 mi ih valve 3i bait is dispesed that Y tion roller directly" ously explained, each of the portions 28 and 28 moves more rapidly during its return stroke than during its working stroke. In the apparatus shown, each idle stroke is completed -before the rotation of the cam terminates the engagement of the cam edge 39' with the plunger of the valve supplying the pressure iiuid effecting the idle stroke. During the period between V-the end of an idle stroke and the beginning of the following working stroke, the corresponding piston 38 or 38 stalls against the rear end of the corresponding piston chamber.

The Apressure fluid supply pipes 35 and 35 lare connected to the respective outlets of two similar constantly operating pumps 45 and 45', so that the two supply pipes are continuously receiving pressure uid from similar sources of such iiuid. As shown, the pumps are rotary pumps of the displacement type, and have a common driving shaft 45. The latter carries a pulley 41 rotated by a belt 48 which runs over the pulley 41 and over the driving pulley of an electric motor 49 the latter normally operating at a predetermined speed. v'Ihe pumps 45 and 45 draw oil or other pressure fluid from an oil tank or reservoir 59 through a `suction pipe l which normally includes a lter (not shown). The pipe 5I is connected to the inlet of the pump 45 by a branch pipe 52, and is connected to the inlet of the pump 45 by a branch pipe 52. The return pipe 31 discharges into the tank 50.

An important feature of the present invention is found in its provision for preventing injury to the apparatus as a result of an overly large increase in the resistance to rotation of the structure rotated through the ratchet wheel l1. Such anv increase may result from an increase in the density of mud engaged by the rake armv Scrapers 5', or from an increase in the amount of mud which has accumulated on the settling chamber floor and increases the load on the motor and tends to increase 'the pressures in the pipes 35 and 35', and tends to slow down the pumps and their driving motor 49. In the preferred form of the present invention, the extent'of permitted increase in pressure transmitted by the pipes 35 and 35' to thev Valves 34 and 34', respectively,` is limited to a predetermined maximum by the inclusion of pressure relief valves 55 and 55 in the pipes 35 and 35', respectively. Those valves are arranged to open and discharge pressure fluid when the pressure therein attains the predetermined maximum desired. As shown, the oil or other pressure fluid then discharged from the pipes 35 and 35' by the relief valves 55 and 55 is returned-to the reservoir 55 vthrough separate outlet pipes 55 and 55', respectively, and through a common return pipe 51 to which each of the pipe outlets 55 and 55 is connected. Advantageously, and as shown, a pressure gauge 58 is connected to the portion of the pipe 35 between the outlet of the pump 45 and the relief valve 55, and a similar pressure gauge 58' is connected to the pipe 35' betweenthe pump 45' and the relief valve 55'.

Additional protection against undesirable operating conditions is obtained by pressure relief valves `59 and 53' included in the pipes 3l and 3l' supplying pressure fluid to vthe cylinders and 2U', to effect the return strokes of pistons 28 and 28'. Each of the valves 59 and 59' is adapted to open on the pressure increase in the corresponding pipe 3l or 3| when the return movement of the associated piston 23 or 28 is interrupted by its engagement with the front end wall of the chamber in which it works. The pressure fluid discharged by valves 59 and 59 is returned to the tank through relief valve outlet connections 59 and 59' to the return .pipe 31.

The valve 34 in the particular form diagrammatically illustrated in Fig. 8, comprises a stationary valve body formed with a cylindrical piston chamber 55 surrounded by three side by side circumferential grooves 56, 61 and 58, each open at its inner edge to the piston chamber.. The valve body is also formed with circular chambers 59 and 15 at its opposite ends wh'ich are larger in diameter than the valve chamber 55. The end chambers 59 and 1l) are connected by a passage l in the portion of the valve body sur-A rounding` the piston chamber 55 and associated annular passages 55, Y51 and 58. The pipes 30, 3i, 35 and 35 are connected to the channels 55 58, 51 and 1|, respectively, through ports formed in the casing or body of the valve 34. The plunger or movable valve member 38 of the valve 54 comprises spaced apart piston portions 12 and 13 working in the valve chamber 5.5, and a valve stem portion at one end of the piston portions 13 of reduced diameter. Said stem portion is slidingly received in and extends through a passage of corresponding diameter in the valve body. As previously stated the valves 34 and 34 may be alike, and in Fig. 8 the valve 34' is shown as comprising parts 55', 55', 51', 68', 69', 10', 1 I 12 and 13', corresponding respectively to the parts 55, 55, 51, 68, 69, 10, 1|, 12 and 13 of the valve 34.

In the position of the valve member 38 shown in Fig. 8 in which its stem portion engages the cam disc edge 39", the pressure fluid passing into the valve through the pipe 35 passes through the channel 51 into the piston chamber 55' through the space between the piston end portions 12 and 13' of the valve 38', and thence through the channel 55' and pipe 3D' into the rear end of the cylinder 20'. In this condition of the valve 34', pressure fluid is exhausted from the front end of the cylinder 25' through the pipe 3l which opens into the circumferential channel 58' which is in communication with the channel '.10' when the movable valve member is in the position shown in Fig.` 8. The channel 10' is at all times in free communication with the transverse .channel 1l' and thereby is in free communication with the outlet 35' andexhaust pipe 31.

In Fig. 8 the valve stem 38Vof the valve 34 is in engagement with the edge 39 of the cam 39, and the right end piston portion 12 of the valve 38 closes communication between the channels 55 and 51, while the left end piston portion 13 of the valve 38 is in such position that the channel 51 is in free communication with the channel 58. In consequence, pressure uid then passes throughthev pipe 3l into the frontend of the cylinder 20 to effect an idle or return stroke of the lever I9. In this condition of the valve 34, pressure fluid may exhaust from the rear end of the cylinder 20 through the pipe 3U, the channel 13, and chamber 69, cross-channel 1l, outlet 36 and pipe 31.

As shown in Fig. 8, the valve member may be formed with its piston portions 12 and 13 so shaped and disposed that as the member passes through an intermediate position the channel 6l is in communication with the adjacent channels 55 and 58 andthe channels 55 and 58 are in communication with the channels 69 and 10, re-

spectively. The liquid supplied by the supply to a piston working in a corresponding one of four hydraulic cylinders 2M, 20D, 20c and 20d. As shown, each pawl 86 has a shank 87 anchored in a chuck or bushing 88, and the latter has a tubular tenon portion secured in the outer end of the tubular piston stern or rod 89 formed integrally with the piston 9|] working in the corresponding hydraulic cylinder. The four hydraulic cylinders are mounted on the stationary framework 80, and are spaced 90 apart about the common axis of the framework Sil and turn-table element. Each of the hydraulic cylinders is formed with aligned upper and lower vertical trunnion pivots 9| adjacent the rear end of the cylinder and journalled in suitable bearings supported by the stationary framework 8U. A spring 9 2 acting between a stationary abutment 93 carried by the framework 8i) and the inner side of each cylinder in front of its trunion pivots, tends to hold each pawl Y86, or some portion of its mechanical connection with the corresponding piston 90, in engagement with a tooth Ila at all times.

In the arrangement shown, the pistons working in each pair of diametrically opposed hydraulic cylinders are given their working strokes simultaneously, and are given simultaneous return strokes during periods alternating with those in' which they make their working strokes. During the periods in which the pistons Working in either pair of diametrically opposed cylinders are making their working strokes, the pistons working in the other pair of cylinders make their return strokes. During each working stroke of each pawl 86, the latter is in engagement with the corresponding tooth lla of the member 19 while the latter is given an vangular movement corresponding to the angular distance between each two adjacent teeth Ila. The supply of oil under pressure to, and the exhaust of oil from the ends of the Various cylinders ZUa-Zd may be controlled in various ways.r For example, each of the teeth lla may successively actuate a control switch mechanism to thereby control the energization of solenoid control valves. As diagrammatically shown inV Fig. 9,-however, the supply of pressure fluid to, and its exhaust from the four cylinders is regulated by control valves 34a and 34h which may be exactly like the Valves 34 and 34' of the construction irst described and which are adjusted by an edge cam 39a shaped exactly like the edge cam 39 of the construction rst described. As diagrammatically indicatedv in Fig. 9, the shaft 46a which carries the cam 39a also ycarries a small gearllla having its teeth in mesh Ywith those of an internal spur gear Hb carried by the turn-table element 19. The teeth of the gear 41a and the gear Hb are of such pitch that the cam 39 makes one complete rotation for each angular advance movement of the element 'I9 corresponding to the angular distance between two adjacent teeth lla.

As diagrammatically shown, the valve 34a has conduit connections 3U and 3l through which oil passes alternately in opposite directions, as it passes through the connections`v 30 and 3|, respectively, of the Valve 34 of the construction iirst described. The conduit connection 30 is connected by a branch pipe 30a to the rear end of the cylinder 2nd, and is connected through a branch 39h to the rear end of the cylinder 20h. The conduit connection 3l has a branch 3|a connected to the front end of the cylinder 29a, and a branch Sib connected to the front end of the cylinder 2Gb. The control valve 34h has 12 connections 30 and 3l' corresponding to the connections 3U and 3|' of the Valve 34 of the construction first described. The conduit connection 3U has a branch 30e running to the rear end of the cylinder 29o and another branch '36d running to the rear end of the cylinder 20d.` The conduit connection 3l has one branch 3Ic running to the front end of the cylinder 20c and another branch 30d running to the front end of the cylinder d. The valve 34a receives oil under pressure and exhausts oil through pipes 35a and 35a, respectively. Similarly, the valve 34h is associated with supply and exhaust pipes 35h and 36h, respectively, as the valve 34 is associated with the pipes 35 and 36 in the construction rst described. The pipes 35a and 35h include pressure relief valves a and 55h, respectively. Similarly, the pipes 3l and 3l of Fig. 9 include pressure relief valves 59a and 59h which serve the purposes of the valves 59 and 59' of the construction rst described, and may be similarly connected to the exhaust piping.

The general operation of the apparatus shown in Figs. 9, l0 and 11 is quite similar to that of the apparatus shown in Figs. 1-8. With the control Valve arrangement shown in Fig. 9, the pair of cylinders 26a and 20h or the pair of cylinders 20c and 20d can do collectively what is done by either one of the cylinders 2 and 2E of the rst construction. With the two cylinders of each pair at opposite sides of the axis of rotation of the structure rotated, the torque producing forces acting on the rotating structure at any one time are in balance, so that they subject the rotating structure to no unbalanced force tending to move the structure transverse toits axis of rotation.

With the valve mechanism shown in Fig. 9, the working strokes of each diametrically opposed pair of cylinders may overlap the working strokes of the other pair, and each of the four cylinders thus contributes to smooth continuous rotation of the rotating structure. The advantage obtained with the arrangement shown in Figs. 1-8 from the fact that each cylinder-is supplied with working fluid from a separate source delivering pressure fluid at a substantially constant volumetric rate, is not lost with the arrangement shown in Fig. 9, since the two cylinders simultaneously supplied with oil under pressure by any one of the conduit connections 30a, 3Ia, 30h, 3lb, operate in synchronism and in phase with one another, and under the same load conditions, so that each takes its half of the pressure fluid then being supplied by the conduit connection.

With each pawl 86 in line with, and rigidly connected to the piston working in the corresponding hydraulic cylinder, the mechanism for applying the torque to the turn-table element 19 is very simple and direct. The line of action of each pawl on the element 19, departs from the tangential only to a relatively small amount, so that each cylinder operates on the element 19 with but little less than the maximum possible power. The physical connection of the pipe 30a to the forward end of the cylinder 20a, as is shown in Fig. l1, and the arrangement of the portions of the pipes 30a and 31d adjacent the cylinder makes it possible to'substantially minimize the stresses impressed on the flexible portions of the pipes by the oscillating movement of the cylinder 20a relative to its supporting structured. rllhe piping to each .of the cylinders 201;, p and 29d may be like the piping to the cylinder 20a in respect to the relative disposition of the pipes and cylinders shown in Fig. l1. With the pawls 86 and their mechanical connections to the corresponding pistons 9D disposed and arranged as shown, each pawl is in continuous engagement with a single tooth Ila throughout each working stroke, and may be in such substantially continuous engagement with said tooth and the following tooth during the following return stroke as lto avoid any significant angular movement of the corresponding hydraulic cylinder about the axis of the pivots 9|.

The pawl and pawl supporting surfaces engaging the teeth l1 are subject to only moderate wear and may be made readily replaceable when necessary, or desirable. As shown, each pawl is provided with a removable bumper plate 94 formed of non-metallic material such as a fibre reinforced plastic which lines the portion of the pawl directly alongside of the end of the tooth Ila with which the pawl is in engagement during its working stroke. The use of such non metallic material cushions the engagement of the pawl with the top of a ratchet tooth.

While in accordance with the provisions of the statutes, I have illustrated and described the best form of embodiment of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of my invention as set forth in the appended claims, and that in some cases certain features of my invention may be used to advantage without a corresponding use of other features.

Having now described my invention, what l claim as new and desire to secure by Letters Patent, is:

l. A sedimentation unit comprising a sedimentation space and including in combination, a stationary supporting structure, a rotating structure mounted in said supporting structure to rotate about a vertical axis, and including a mud rake in said space, hydraulic motor drive means including a pawl and ratchet mechanism for rotating said rotative structure comprising a ratchet wheel and a plurality of oscillating pawls each adapted to engage said wheel and subject the latter to a rotative force when moving in one direction during each oscillation, a separate hydraulic cylinder and piston longitudinally movable therein associated with each pawl, a mechanical connection between each piston and as sociated pawl through which said pawl may be moved in a driving direction to rotate said rotative structure when liquid under pressure is supplied to one end of the cylinder containing said piston and may be given a return movement when liquid under pressure is supplied to the other end of that cylinder and arranged to make the working stroke of each pawl overlap a portion of the working stroke of another pawl, and mechanism for passing liquid under a regulated pressure alternately into the opposite ends of each cylinder and for exhausting liquid from each end of each cylinder during periods in which liquid under pressure is passed into the other end of the cylinder, said mechanism comprising a separate adjustable control valve associated with each cylinder and having an inlet, a separate conduit connection between said valve and each end f cylinders simultaneous working strokes 14 of the associated cylinder, and means operating in timed relation with the rotative movement of said rotative structure for adjusting said valve to alternately connect each of said .conduit connections to the inlet of said control valve, and mechanism for continuously supplying liquid ,unfder pressure at the same volumetric rates to the different control valves, the last mentioned mech.- anism including a separate source of liquid under pressure connected to each control valve and passing liquid to the latter at a regulated vol,-

umetric rate.

2. A sedimentation unit as specied in claim 1, including a separate pressure relief valve associated with the conduit connection between each control valve and the said other end of the associated cylinder, and operating to prevent the pressure in said connection from exceeding a predetermined maximum, and a separate pressure relief valve through which the separate source of liquid under pressure connected to the last mentioned control valve passes liquid to the latter.

3. A sedimentation unit as specified in claim 1, in which each cylinder is pivotally connected to said supporting structure to oscillate about an axis parallel to the axis of rotation of said rotatable member and in which the mechanical connection between each pawl and the associated piston comprises a ratchet lever pivoted to rotate about said axis of rotation and to which said pawl is pivoted and in which the corresponding piston has a stem rigidly connected at one end to said piston and rigidly connected at its opposite end to said lever.

4. A sedimentation unit as specified in claim 3, in which each cylinder and associated lever and mechanical connection are so formed and arranged that the ratio of angular movement of each lever to the longitudinal movement of the corresponding piston is greater in the initial portion of the working stroke movement of the piston toward said ratchet end of the corresponding cylinder than in the major following portion of said working stroke movement.

5. A sedimentation unit as specified in claim 1, in which the hydraulic cylinders are arranged in pairs with the two cylinders of each pair mounted on said supporting structure at opposite sides of the axis of rotation of the rotating structure, and in which each adjustable control valve is associated with each cylinder of a corresponding pair of said cylinders and supplies pressure fluid alternately to the opposite ends of said cylinders as required to give the pistons working in the two and simultaneous return strokes.

6. A sedimentation unit comprising in combination, stationary supporting means, a rotatable structure mounted in said supporting means to rotate about a xed axis and including a series of teeth extending circularly about said axis, a plurality of pawls cooperating with said teeth to form a pawl and ratchet mechanism adapted to rotate said structure about said axis when said e pawls are oscillated, a separate hydraulic cylinder associated with each pawl, a reciprocating piston in each of said cylinders, a mechanical connection between each piston and the associated pawl oscillating the latter when said piston is reciproq cated, a separate control valve associated with each cylinder and having an inlet for liquid under pressure, an exhaust outlet and a separate conduit connection to each end of the associated cylinder, means adjusting each control valve in timed relation with the rotative movement of said rotating structure to alternately connect its conduit connections to its inlet and to connect each of said conduit connections to said exhaust outlet when the other of said conduit connections is connected to said inlet, a separate pressure ren lief valve connected to each control valve and having a relief outlet and including means for opening and closing said relief outlet as the Dressure in said control valve rises to and falls below a predetermined maximum, and means connected to the inlet of each pressure relief valve and sup plying liquid under pressure thereto at a constant volumetric rate.

CHARLES HAROLD SCOTT.

16 REFERENCES CITED The' following references are of record in the le of this patent:

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